1. Field of the Invention
The invention relates to aqueous dispersions, with which the concrete can be made more flexible and with which the shrinkage of the concrete mixture can be reduced during setting and with which it is possible to use filling agents in the concrete mixtures hitherto regarded as toxic to cement.
2. Description of the Related Art
Due to growing industrialization in most countries of the world and the desire for mobility of human beings, street and road construction is growing in importance. The most desired road construction material is bitumen. Bitumen has the advantage of being flexible enough to adapt to the movement of the subsoil. Therefore roads, which contain bitumen, do not form any cracks and/or edge projections. Furthermore, a bitumen layer has proven to be exceptionally resistant to abrasion enabling streets with a bitumen layer to last for a long time. The disadvantage of bitumen is its very high price and its lack of availability in many countries. Additionally, bitumen is not suitable as a construction material for road construction purposes in many countries of the south and far eastern hemisphere, due to the fact that it lacks a resistance to heat.
An alternative road construction material is concrete. In comparison to bitumen, concrete is remarkably lower in price, and the kind of materials needed for concrete mixtures, e.g., cement, water and filling agents such as sand, are more available than bitumen in large parts of the world. Additionally, concrete does not turn soft even at extreme exposure to sunlight. To be able to build roads made of concrete, the subsoil under the concrete slab has to be very solid. Otherwise, the concrete slabs will either break or they will settle in such a way that edge projections may occur. Broken slabs or edge projections may cause extreme stress to motor vehicles travelling on the road, and are annoying to drivers. The process of hardening the subsoil is an extremely cost effective procedure, whereby the native soil is replaced by a compressible material, for example, sand.
There have been many tests with additives to make concrete as flexible as bitumen. AU-A-35121/93 shows a mixture which is added to a concrete mixture to make concrete more flexible and reduce shrinkage during setting. The mixture mainly consists of two components: mainly of chloride salts and an alkali silicate (waterglass), preferably sodium silicate. The two components are premixed and then added to a concrete mixture made of cement, water and sand. The final mixture can be used, for example, in road construction. This procedure has the disadvantage that the two components of the mixture react with each other during the premixing process. Additionally, the silicate starts setting before it comes into contact with the concrete mixture so that the actual effect of this mixture in the concrete mixture is limited. Furthermore problems may arise because waterglass is treated as a dangerous substance and may only be processed by those using gloves, safety glasses and an apron. These safety precautions also have to be taken during transport.